Acid resistant copper alloys



Patented June 29, 1937 UNITED STATES PATENT OFFICE ACID RESISTANT COPPER ALLOYS No Drawing.

Claims.

This invention relates to acid resistant copper alloys; and it'comprises as a quaternary alloy of copper a physically homogeneous solid solution of small grain size and of good tensile strength 5 without brittleness combined with easy Workability and containing 2 to 3 per cent each of nickel, aluminum and tin with 94 to 91 per cent copper; all as more fully hereinafter set forth and as claimed.

Copper metal is not attacked by acids or alkalies in the absence of oxygen. It is, however, oxidized by moist air and in the presence of oxygen the metal is corroded and dissolved by most acids. Pure copper is so. soft that it is diflicult to machine. Its tensile strength is comparatively low. For use as sheets, bars, wire, tubes, rivets, rods, bolts, nuts and the like, copper is mostly alloyed with other metals. In these alloys the inherent properties of copper metal are drasticalnn 1y changed. It is an object of the present invention, by'alloying the copper with other metals, to increase the strength and hardness and lessen the ductility and malleability of copper'metal to the proper extent to make it=practically work- 0-, able by modern commercial-machine methods and to increase its resistanceto'acid oxidation attack without interfering with the workability of the metal and without making it brittle.

I have found that when copper is alloyed with an about 6 to 9 per cent of the three alloying metals, nickel, aluminum "and tin together, and when these three alloying metals are present in substantially equal'proportions, these objects are attained: a copper alloy is produced of excellent mechanical properties, high resistance to corrosion and of outstanding excellence for many purposes such, as heat exchanger tubing. The alloy of copper with small amounts of nickel, aluminum and tin is greatly superior, in the 0 above identified respects, to those composed of copper, nickel and aluminum, or of copper, nickel and tin. For example, I have found that an acid resistant, workable alloy of 90 to 94 per cent copper 3 to 5 per cent aluminum and 3 to 5' per cent nickel, is greatly improved by replacing substantially equal fractions of both the aluminum and the nickel with tin.- The total percentage of the alloying components is not substantially changed but the replacement by tin of about one-third of the aluminum and one-third of the nickel, adds to the acid oxidation resistance of the metal alloy, improves its workability by modern machine methods and makes a generally improved metal for use in the form of sheets, bars, wire, tubes, rivets, rods, bolts, nuts,

etc. In particular, the quaternary alloy of cop- Application October 13, 1936, Serial No. 105,442

per, nickel, aluminum and tin in the stated proportions gives an improved metal for use in making condenser tubes. As stated, the quaternary alloy is more resistant to acids, alkalies and oxidation-corrosion, is stronger, less brittle, and 5 more readily workable than the ternary alloys of copper with nickel and aluminum.

This quaternary alloy of copper with small amounts of nickel, aluminum and tin appears to be a true solid solution of the four metals. The physical structure of the metal after heat treatment of the cast metal by usual methods is made. up of small size grains, usually not larger than 0.012 mm., and appears to be completely homogeneous.

I find that the total combined percentage of the three alloying metals added to the copper should be kept within the range of 6 to 9 per cent of the alloy, the copper ranging between 94 and 91 per cent. With substantially more than 9 per cent of Ni, Al and Sn combined and less than 91 per cent copper, the metal becomes brittle and unworkable and with more than 94 per cent copper and less than 6 per cent of Ni, Al and Sn the metal is too soft and low in tensile strength. However, some latitude is allowable in the respective proportions of the three alloying addi tions. For example, the aluminum may run slightly below 2 percent of the alloy and the nickel and tin proportionately above 2 per cent each. Small amounts of other metals, as for example iron and manganese, existing as impurities donot alter the properties ofthe alloy, so long as the relative proportions of the four metals in the quaternary alloy are not materially affected.

In making a copper alloy resistant to acid ox- .idation attack and also strong and workable, it has been known that aluminum and nickel to.- gether in small ratios to the copper are effective. 0 Copper of course has been alloyed with various large and small proportions of nickel and in these copper-nickel alloys small percentages of tin, running from 1 per cent to around 5 per cent, have improved both the workability and also the 5 resistance to oxidation and acid corrosion.

The quaternary alloy is made by melting the constituent metals together in, aclay graphite crucible heated in an electric furnace. Advantageously pure nickel shot may be placed in the 50 bottom of the crucible and an alloy of 95 per cent copper with 5 per cent aluminum melted down over the nickel shot with suflicient pure copper added to give the required ratio. The mixture in the crucible is held under a charcoal Rock- Lbs/sq. Per- 11 Gauge in. tencent we Description inch sue Glen's. Es Remarks strength 2 100 g) No.8 hard .005 102,000 2.0 B as Annealed 8!; W C- 035 70, 23. 0 B 77 Annealed at 050 C- .035 32.0 B 01 Quenched from 035 46,(I)0 53.0 B 33 quenched aged 2 .005 41, too 42. 0 a 43 hrs-( D 050 C. Qlgg ryi chad rolled 047 90,000 4. 0 B 92 Quen ched rolled .041 50,000 38.0 a 5'! Completely- 50%, aged 2 hrs. recrysta moi iud,gr.siu

.012 mm. Qggnchod rolled 022 107, 2.0 B W 'Quenc hed rolled on as, 000 as. o B 04 Completel 76%,aged2hra6 rccrysta 650 C. zed,gr.si1.e

cover to complete the fusion and the tin is added with thorough admixture before skimming the melt and pouring into oiled. warm cast iron moulds. It is usually advantageous to-deoxidize the melt just before pouring by a small addition of magnesium.

The following examples A, B and C are given of the quaternary copper base alloys of the present invention.

Alloy A analyzes as 93.85 per cent copper, 2.43 per cent tin, 2.31 nickel and 1.64 per cent aluminum. The tensile strength is good, the metal, exhibits an exceptionally fine-grained structure and has a high acid resistance. Metal of 0.035

gauge. and of 8 degrees hardness has a tensile strength of 102,000 pounds per square inch with 2 per cent elon ation. The tensile strength drops on annealing and quenching but can be reinstated by reduction in rolling.

Tabulated, the properties of this alloy are:

Alloy B, a second alloy, analyzes 92.57 per cent copper, 2.09 per cent tin, 2.32 per cent nickel and 2.51 per cent aluminum with 0.57 per cent manganese. The tin is a little less and the aluminum a little higher, but the alloy has properties quite similar to those of alloy A There is but little tendency for these alloys to become hardened by the aging heat treatments.

The third alloy C analyzes 90.89 per cent copper, 3.16 per cent tin, 2.23 per cent nickel and 3.23 per cent aluminum. In this alloy the copper is somewhat less and there are variations in amount 01' the three metals. The alloy shows the following characteristics:

Lbs/sq. in. Percent Rockwell Description 2%}? tensile along. No.

' strength 2" 100 kg.)

Quenched from 650 C-.--. 025 68, 10 40. 0 B 07 Quonched aged 2 hrs 6 375 0. 70,800 31.0 B 71 quenched aged 2 hrs quenched rolled 119, 700 2.0 B 99 quenched rolled aged 2 hrs Quonched tolled 75 125, 000 1. 0 B 101 quenehzmli a lied 76% What I claim is:-

1. An acid and oxidation resistant physically homogeneous and easily workable copper alloy consisting substantially of copper, nickel, aluminum and tin in the proportions 0! Per cent Copper 94 to 91 Nick 2 to 3 Aluminum 2 to 3 Tin 2 t0 3 about 6 per cent nickel and aluminum in approximately equal proportions, characterized by having approximately'one-third ot the nickel and one-third of the aluminum replaced by tin.

5. A copper-nickel-aluminum-tin alloy composed of about 94 per cent copper alloyed with a total of about 6 per cent of nickel, aluminum and tin in approximately equal proportions.

WILLIAM B. PRICE. 

